Cylinder Head Bolts

I had a 1952 MG. When I had to change the head gasket, the head bolts had to be replaced with new ones. I tried to reuse the old bolts and ended up with several sheared bolts. Metallurgy wasn't great back then.

Excellent Ozzb precise and to the point. Not even any need for other to responde.

Most cylinder head bolts are "torque to yield". When properly tightened, the clamping force is more precise then with old style bolts torqued to a specific numeric value.

The differance between a set screw and a bolt is that a bolt is threaded for about 1 inch of it's length and the remainder of it's length is to a diameter of the thread but in a bar form.

A set screw is threaded all the way to the bottom of it's head. So a 10mm bolt will only be an 8.159 mm diameter bolt. The threads inside of the cylinder head are not doing anything and in theory could be ground off.

These set screws are 110mm long with a number 45 TX star head that has a flanged washer formed to the bottom of it, so the washer and bolt head are one piece.

How much compression can you put on to the head gasket is the real question. With a 1,5mm pitch on a 10mm bolt and a half a turn 180degrees the compression is 0.75mm plus the toque load.

So why use a toque setting at all. Why not say do the bolts up to finger tight and then tighten it up 3/4 of a turn(260 degrees). or 1.125mm.

The strain on the threads will depend on how Meany threads are in the cylinder block. the deeper the bolt goes into the block the more threads are used so the less of a load on each thread.

As the slandered temperature for manufacturing components is 20degrees Centigrade.

If the components are assembled at 0 degrees ( freezing point ) Then the metals would have contracted by about 2 thou per inch. So when the metal reaches its operating temperature it will have expanded and increasing the load on the bolts.

Rick took the words out of my mouth and received some undeserved OTs for it. In my book, a set screw doesn't have a head. If a threaded fastener has a head, it is not a set screw. Guest is correct in that there are other torquing procedures such as finger tight, then XX degrees of rotation. That's how oil filters are installed. The engine manufacturer recommends his procedure for a reason. If you don't agree with it, you are free to change the method. As far as temperature is concerned, the final average compression of the gasket will be a function of the initial tension of the bolts, the initial temperatures of all the components, and the differential expansion of the block, head, and bolts. If the block, head and bolts are all iron and steel, the differential expansion will be close to 0, and the tension will not change with temperature. If the head is aluminum and the other 2 components are steel or iron, fastener tension will be a function of temperature.

Both of the screws mentioned ones with heads and without heads are set screws because they are threaded all the way up.

The type that do not have a head are more commonly known as GRUB Screws. The applications for grub screws is in retaining sleeved bearings in position on a shaft. Or on electric motors to retain the pulleys. on some of these pulleys the boss is about 1.1/2 inches in diameter and the set screw needs to be screwed down on to the shaft and as the screw is about 1/2 inch long it would not reach the shaft if it had a head on it.

Some times two screws can be used to lock against each other in the pulley boss. This is termed as SCOTCH LOCKING. it acts in the same way as using two nuts locked against each other to stop them from coming loose. But in reality this dose not happen as the second nut removes the load on the first nut and turns it into a glorified spacer.

The set screw that has a square on it's top can be found on lathe tool post holders to enable the quick setting of the cutting tools.

But yes if the screw is threaded all of it's length then it is a set screw. With or without a head.

With this type of job, do everything exactly the way the book tells you. This way you will not have to do the whole lot again in a month or so. These bolts stretch on the final tightening sequences they will not bottom out even if the head has been skimmed before. (there is a limit to the ammount that can be skimmed and this is taken into consideration when the bolts are manufactured). So use new bolts preferably all OEM parts and send the head for skimming if it needs it and don't forget to change the thermostat, flush the coolant system etc etc etc.... Happy motoring!